Exhaust emission purifying apparatus for engine

Abstract

An exhaust emission purifying apparatus has a NOx reduction catalytic converter in an exhaust passage of an engine, for purifying nitrogen oxides in the exhaust gas by reduction with urea aqueous solution; an injection nozzle injecting the urea solution toward an exhaust upstream side of the converter in the exhaust passage; and fins disposed on an exhaust upstream side of an injection position of the urea solution in the injection nozzle, for generating a spiral swirling flow of the gas swirling about a center corresponding to the central axis of an exhaust pipe. The swirling flow generated in the exhaust gas prior to the injection-supply of the urea aqueous solution promotes mixing of the solution with the gas to thereby promote the hydrolysis of the urea solution. And the exhaust gas and ammonia generated from the urea solution are uniformly mixed together.

1. An exhaust emission purifying apparatus for an engine, comprising:
 a reduction catalytic converter disposed in an exhaust passage of said engine, for purifying nitrogen oxides contained in the exhaust gas by reduction through reacting with a reducing agent; 
 an injection nozzle for injection-supplying the reducing agent at a position in said exhaust passage on an exhaust upstream side of said reduction catalytic converter; and 
 a swirl-flow generating means disposed on an exhaust upstream side of an injection position of the reducing agent in said injection nozzle, for generating, in the exhaust gas, a swirling flow which spirally swirls about a center corresponding to a central axis of said exhaust passage, 
 wherein said swirl-flow generating means comprises a plurality of fins which is provided in said exhaust passage in a manner such that said fins extend, respectively, defining a predetermined angle with respect to a linear direction in which the exhaust gas flows from the exhaust upstream side toward an exhaust downstream side, 
 wherein said fins are formed by pulling up a corresponding number of fin-forming portions of a thin plate of a shape substantially the same as a cross section of said exhaust passage, said fin-forming portions being defined by cuts given to said thin plate, 
 wherein said reduction catalytic converter is formed to have a diameter thereof larger than the cross section of the exhaust passage on the exhaust upstream side thereof and on the exhaust downstream side of the swirl-flow generating means, and 
 wherein said passage is formed such that an edge portion thereof is expanded in a bell-mouth shape increasing a diameter thereof toward the exhaust downstream side, at an exhaust gas inlet portion to said reduction catalytic converter. 
 
   
   
     2. An exhaust emission purifying apparatus for an engine, comprising:
 a reduction catalytic converter disposed in an exhaust passage of said engine, for purifying nitrogen oxides contained in the exhaust gas by reduction through reacting with a reducing agent; 
 an injection nozzle for injection-supplying the reducing agent at a position in said exhaust passage on an exhaust upstream side of said reduction catalytic converter; and 
 a swirl-flow generating means disposed on an exhaust upstream side of an injection position of the reducing agent in said injection nozzle, for generating, in the exhaust gas, a swirling flow which spirally swirls about a center corresponding to a central axis of said exhaust passage, 
 wherein said swirl-flow generating means comprises a plurality of fins which is provided in said exhaust passage in a manner such that said fins extend, respectively, defining a predetermined angle with respect to a linear direction in which the exhaust gas flows from the exhaust upstream side toward an exhaust downstream side, 
 wherein said exhaust passage is formed to be separable in a plane orthogonal to the flow on the exhaust upstream side of said injection nozzle, and 
 wherein said fins are formed by pulling up portions of a gasket which are defined by cuts given to the gasket interposed between flanges which connect separated portions of said exhaust passage to each other. 
 
   
   
     3. An exhaust emission purifying apparatus for an engine, comprising:
 a reduction catalytic converter disposed in an exhaust passage of said engine, for purifying nitrogen oxides contained in the exhaust gas by reduction with a reducing agent; 
 an injection nozzle for injection-supplying the reducing agent at a position in the exhaust passage on an exhaust upstream side of said reduction catalytic converter; 
 a partition plate disposed on an exhaust upstream side of said injection nozzle to traverse said exhaust passage, which is provided with, on a center portion thereof, a swirl-flow generating means for generating a swirling flow which spirally swirls, in the exhaust gas passing through said exhaust passage, and is provided with discharge holes which are formed in scattered manner in a peripheral region of said swirl-flow generating means, for permitting the exhaust gas to flow from an upstream side toward a downstream side via said discharge holes; and 
 a coupling exhaust pipe which constitutes a part of said exhaust passage and is jointed to said partition plate while including said swirl-flow generating means therein, said coupling exhaust pipe being formed with, on a side face thereof in the vicinity of said swirl-flow generating means, exhaust gas introduction holes for introducing the exhaust gas flowing out of said discharge holes of said partition plate into said coupling exhaust pipe. 
 
   
   
     4. The apparatus according to  claim 3 , wherein said swirl-flow generating means of said partition plate comprises a plurality of fins which is formed, by making a plurality of cuts so that a side extending in radial from a center portion of said partition plate becomes a folding line, and by folding an outer edge portion of each of the cuts toward the exhaust downstream at a predetermined angle, thereby generating, in the exhaust gas, the swirling flow which spirally swirls. 
   
   
     5. The apparatus according to  claim 4 , wherein each of said exhaust gas introduction holes of said coupling exhaust pipe is formed to be positioned, at an end portion thereof on the exhaust upstream side, on the exhaust upstream side of a tip end portion of each of the fins of said swirl-flow generating means.